Already auditioning for that role is an eclectic group of ambitious Democrats, including three senators who appear all but certain to run: Kamala Harris of California, Elizabeth Warren of Massachusetts and Cory Booker of New Jersey. All three have moved well past the point of simply weighing a candidacy, and are assembling the infrastructure for a campaign as they prepare to make their final decisions.

Two potentially formidable entrants, Senator Kirsten Gillibrand of New York and Mayor Eric Garcetti of Los Angeles acknowledged this week that they are considering campaigns. And Gov. Steve Bullock of Montana was in New York in the days after the election meeting with wealthy party donors, introducing himself as a dark horse from a red state with the ability to reach out to rural America.